It is becoming common for whole blood collected from a donor to be separated into blood component preparations, such as an erythrocyte preparation, a thrombocyte preparation, and a blood plasma preparation, stored and then provided for transfusion. Since microaggregates and leukocytes included in these blood preparations cause various side effects of blood transfusion, many methods of removing these undesirable components before blood transfusion and then performing transfusion, or performing transfusion with preparations with undesirable components having been removed after blood collection and then temporarily been stored, have been widely used.
Among methods of removing these undesirable components from blood preparations, treatment of blood preparations through a blood processing filter is most typical. Two types of blood processing filters are used; one is what includes a filter element made of nonwoven fabric or a porous body equipped in, for example, a flexible container as described in Patent Literatures 1 to 5, and the other is what includes the filter element equipped in a hard container made of polycarbonate or the like.
Typically, for treatment of a blood preparation through a blood processing filter, a blood preparation bag containing the blood preparation to be processed is connected to an inlet of the blood processing filter, the blood preparation bag is placed at a position higher than the blood processing filter by approximately 20 to 100 cm, thereby introducing the blood preparation from the blood preparation bag into the blood processing filter due to the action of gravity. On the other hand, a recovery bag for storing a filtered blood preparation is connected to an outlet of the blood processing filter, and the recovery bag is placed at a position lower than the blood processing filter by approximately 50 to 100 cm, thereby storing the filtered blood preparation into the recovery bag due to the action of gravity. At this time, a pressure loss occurs due to the resistance of the filter element, in a space in the blood processing filter container on the inlet side of the filter element, thereby causing a positive pressure. On the contrary, in a space on the outlet side of the filter element, the blood preparation flows from the outlet, thereby causing a negative pressure.
Since a blood processing filter with a flexible container as shown in Patent Literatures 1 to 5 has a container that is flexible, the space on the inlet side swells like a balloon owing to a positive pressure, and the filter element is pressed against the outlet side of the container. On the other hand, in the space on the outlet side, the container is in close contact with the filter element owing to the negative pressure, and the state is brought into that where the opening of the outlet is blocked. That is, since blood tends to flow from the inside of the filter but the opening is blocked, it is difficult for the blood to flow out.
On the contrary, a blood processing filter through use of a hard container does not largely deform even during filtering, and the state is not brought into that where the filter element is pressed against the outlet side to block the opening of the outlet. Such a hard container includes an inlet-side container element and an outlet-side container element which are fitted with each other, and rib-shaped convexes provided for the inlet-side container element and the outlet-side container element are pressed against each other, thereby clamping the outer edge portion of the filter element.